White rust is a fungal disease that is easily spread to surrounding plants.
Fungi is reproduced by producing spores that are tiny microscopic cells, each is capable of becoming a fungus, thus establishing a new colony. It is most commonly found on cruciferous vegetables, as well as sweet potatoes, beets and spinach. It is known to affect Pohuehue (beach morning glory) too.
Description:
Its appearance is chalk white, powdery pustules with raised spore masses. These are mostly found on the underleaf. You may also notice the irregular yellow areas (chlorotic lesions) on the upper leaf surface. It is also found on the petiole. White Rust causes leaf loss, bloom reduction and stem die back.
Causes:
- Cool dewy nights and warm humid days are ideal for fungi development.
- Poor air circulation as well as how water is applied from spraying or rain can also contribute to the problem.
Control and Treatment of White Rust Disease:
- Sanitation.
- Remove any debris under plants where spores like to hide.
- Reduce leaf moisture by choosing drip irrigation instead of sprinkler.
- Choose resistant strains of plants.
- Encourage proper air circulation, by allowing enough space in between plants.
- Crop rotation every 3 years.
Treatment:
Prune any infected areas from any plants and dispose of them in a sealed bag. Be sure to disinfect all garden tools used in the process. Adding a thick layer of mulch can prevent splash back on leaves. There are no fungicides specifically for White Rust. Choosing a fungicide that can treat Downy Mildew is sometimes effective for White Rust.
Fungicides need to be applied as soon as fungi appear on the plant. Recommended fungicides include those with active ingredients azoxystrobin: methyl, cyazofamid, mefenoxam, and pyraclostrobin. Read and follow all label directions.
There are some organic options for treatment of rust including Neem oil, and other store bought organic solutions.
In summary, using best cultural practices are key to prevent white rust from developing in the first place. By promoting healthy roots from deep watering, proper spacing with good airflow, the plant will have a better defense against any diseases in general.
References:
https://ipm.ucanr.edu/agriculture/cole-crops/white-rust/
https://ipm.illinois.edu/diseases/rpds/960.pdf
https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/diseases/white-rusts
MM/JRS – 5.21.23
